Method and apparatus for evaluating the performance characteristics of endoscopes

ABSTRACT

An apparatus for evaluating performance of a test endoscope includes a plurality of light sources, each generating a respective beam of light which is transmitted through the test endoscope. The apparatus further has a grid formed with a plurality of evenly spaced and uniformly sized pinholes intercepting a beam of light. The grid is utilized to perform a field of view, image quality, distortion, depth of field and an angle of view tests of the test endoscope. The apparatus further has a fiber optic light guide having one of its ends bifurcated and designed so that the bifurcated ends have the same output for evaluating light transmission through the test endoscope.

PRIOR APPLICATION

This application is a co-pending application of U.S. application Ser.No. 09/563,866 entitled “Rigid Telescopic Inspection System” which isfiled concurrently therewith, and is hereby expressly incorporated byreference as part of the present application.

FIELD OF THE INVENTION

The present invention relates to the testing, appraisal, and comparisonof endoscopes by using an array of targets including a grid of evenlyspaced pinholes to measure at least the image quality, field of view,distortion, and depth of field of an endoscope, a diffuse buttranslucent white target, a single pinhole target and a detector formeasuring luminous flux.

BACKGROUND OF THE INVENTION

The heart of an endoscopic system is in its endoscope. There are twooptical types—those which utilize lenses for image forwarding andformation, and those which utilize fiber optic bundles for forwardingthe image. The former is usually referred to as a “rigid” endoscope, andthe latter as a “flexible” endoscope. In all cases, the elements of theendoscope are carefully installed and aligned by the manufacturer so asto present the best image to the ocular piece, or to the camera, aspossible.

The performance characteristics of the individual endoscope are ofimmediate and very intimate importance to the surgeon. Thus, the surgeonis to be aware, before the procedure, that the endoscope can inherentlydeliver the quality of image he requires, and that if it inherently hassuch quality, the instrument is in good enough condition that it candeliver that quality.

Depending on the inherent design of the endoscope, the specificinstrument might not provide the magnification, clarity, depth of fieldand resolution which would be required, even if it appears undamagedfrom a cursory inspection.

Then it is an unfortunate fact that actions apart from its actual use inthe patient such as handling, transporting and cleaning, the endoscopemay have become misaligned or otherwise damaged. A resulting inabilityto resolve an area of the field should not first be discovered by thesurgeon while the endoscope is inserted in the patient during anendoscopic procedure, as this may result in adverse consequencesincluding additional surgery costs, surgery cancellations and increasedrisk to the patient.

What is desired, therefore, is an apparatus for evaluating the opticalperformance of an endoscope that utilizes a minimal number of measuringdevices for performing a wide variety of optical tests. Also desirableis an apparatus for evaluating the optical performance of an endoscopethat utilizes a grid of evenly spaced pinholes to measure the imagequality, field of view, distortion, and depth of field of an endoscope.Providing an apparatus for automatically evaluating the opticalperformance utilizing a bifurcated fiber optic cable to preciselymeasure transmission of illumination fibers without manual interventionduring a test is also desirable is also desirable. A method forautomatically performing a series of tests on an endoscope and forcomparing the results of these tests with a set of standardizedparameters is also desirable, as is an apparatus for visually displayingthe results of this comparison.

SUMMARY OF THE INVENTION

An apparatus and method according to the invention achieve it bygenerating beams of light which are transmitted through a distal end ofan endoscope towards a proximal end of the endoscope. As a result,output signals indicative of one or more performance characteristicsmeasured by a variety of tests are generated in response to signalscorresponding to one or more of the conducted tests.

Particularly, a combination of a grid target, a diffuse but translucentwhite target, a single pinhole target and a detector for measuringluminous flux is capable of performing a variety of tests. This varietyof tests includes measuring a field of view, geometrical distortion,angle of view, image quality at single and various object distances,percentage light transmission through illumination fibers, relativelight transmission and illumination intensity across the field of view.

According to one aspect of the invention, a grid target has a pluralityof pinholes and is utilized to measure the image quality, field of view,distortion, and depth of field of an endoscope to be tested. Thus,utilizing a single target which is provided with a plurality of evenlyspaced pinholes, each having a uniform size, can make a variety ofmeasurements.

In accordance with another aspect of the invention, a bifurcated fiberoptic light guide attached to a light source is utilized to measureillumination transmission efficiency. The light guide is specificallydesigned so that it the output of one of the bifurcated ends end isknown, then so it the output of the other. Thus, measuring the power outof the one unattached bifurcated end of this guide light and measuringthe power out of the endoscope to which the other bifurcated end isattached one can calculate the transmission of the scope.

A number of tests can be automatically selected by utilizing a controlsystem of the inventive device which allows a user to bypass any of theregular tests. The control system includes a central processing unitregulating the sequence of operations leading to performing any of orall of the regular optical tests. Images of the results can appear on amonitor and be compared to the standardized results stored in thesystem's database. Some of the images can be color-coded to assist auser in easy identification of the optical performance of the testedscope.

The apparatus in accordance with the invention allows a user to test anendoscope by comparing its optical performance with a standard endoscopewhose parameters are stored in database. Alternatively, an endoscope canbe tested without being compared with the standard one. Also, a set ofnew parameters of an endoscope to be tested can be added to database ofthe apparatus.

Accordingly, it is an object of the invention to provide a method andapparatus for evaluating the optical performance characteristics of afiber optic endoscope.

Still another object of the invention is to provide an apparatus formeasuring the mage quality, field of view, distortion, and depth offield of an endoscope by utilizing a single target having a plurality ofpinholes.

Yet another object of the invention is to provide a method and apparatusfor measuring illumination transmission of an endoscope by utilizing abifurcated fiber optic light guide.

It is a further object of the invention to provide a method foroperating an apparatus for evaluating the optical performance of anendoscope in a variety of automatic and manual modes.

It is still another object of the invention to provide a method foroperating an apparatus for evaluating the optical performance of anendoscope to assist a user in conducting the evaluation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an apparatus in accordance with theinvention.

FIG. 2 is a diagrammatic view of an apparatus shown in FIG. 1.

FIG. 3 is an isometric view of a carousel carrying a variety of targetsof the apparatus of FIG. 1.

FIG. 4 is a schematic view of a grid target carried by an apparatus ofFIGS. 1 and 2.

FIG. 5 is a graphical representation illustrating measurement of a fieldof view test.

FIG. 6 is a graphical representation illustrating measurement of ageometrical distortion test.

FIG. 6A is graph illustrating the geometrical distortion.

FIG. 7 is a graphical representation a spread point function of animaged pinhole.

FIG. 8 is a graphical representation of an angle of view of anendoscope.

FIG. 9 is a graphical representation illustrating a measurement of theangle of view.

FIG. 10 is a flow chart illustrating the procedural steps for performingan image quality, field of view, distortion, and a depth of field testsof an endoscope to be tested by an apparatus of FIG. 1.

FIG. 11 is a schematic view of a bifurcated cable in accordance with anapparatus shown in FIG. 1.

FIG. 12 is a flow chart illustrating the procedural steps for relativeimaging system transmission test by an apparatus of FIG. 1.

FIG. 13 is an exemplary display of a graphical user interface providedby a computer of FIG. 2 for evaluating results of a series of tests.

DETAILED DESCRIPTION OF THE DRAWINGS

As shown in FIGS. 1-2, a telescope inspection system 20 for evaluatingthe optical performance of an endoscope according to this inventionincludes a casing 22 having a bottom 23 and provided with a closure 25which can close the casing during examination of an endoscope.

The casing 22 houses a testing station 24 which includes a turntable 26rotatable to a known nominal angle of a standard endoscope, a linearlymovable carousel support 28 and a carousel 30 carrying a plurality oftargets 32 and capable of rotating independently from the turntable 26.The casing further encloses an endoscope support station 34 and analignment station 36 extending between the endoscope support and testingstations.

As better illustrated in FIG. 2, the inspection system is constructedfor testing any of a plurality of endoscopes 50 mounted on the endoscopesupport station 34 and having different physical and opticalcharacteristics. The inspection system 20 is designed to perform avariety of tests on an endoscope by comparing it with a standardendoscope which has its reference parameters stored in memory of acentral processing unit (CPU) 44. Preferably, a variety of standardendoscope types is manufactured by Karl Storz, and each of them has arespective set of reference parameters stored in the system. However,the inspection system 20 is also capable of evaluating the opticalperformance of new types of endoscopes in response to a set ofparameters given by a user. Images and results of the tests aredisplayed on a monitor 46 and can be printed by a printer 48.

Examination of the endoscope 50 is performed by selectively displacingthe carousel 30 in such a way that each of the targets is controllablypositioned at a nominal object distance with respect to a distal end 52of the endoscope to conduct a respective optical test. The term “target”broadly describes any of the various devices used for receiving andreflecting a transmitted beam to evaluate the physical and opticalparameters of the endoscope 50. Cumulatively, the targets perform thefollowing tests: a field of view, geometrical distortion, angle of view,image quality at single and various object distances, percentage lighttransmission through illumination fibers, relative light transmission ofimaging system and illumination intensity across the field of view. Thenumber of tests can be increased, but those listed above are the mostcritical tests that typically provide thorough examination of anendoscope.

The array of targets may have a various number of targets depending on aparticular test to be conducted. As better shown in FIG. 3, the array 32includes a diffuse but translucent white target 60, a grid with pinholestarget 62, a detector 64 to measure optical power or luminous flux and asingle pinhole target 66.

In accordance with one aspect of the invention shown in FIG. 4, the gridtarget 62 capable of performing at least the image quality test, fieldof view, distortion, and a depth of field of the endoscope 50 is formedwith a plurality of evenly spaced pinholes 63. Given only as an example,the grid target 62 is a 6″×6″ square plate made of glass. Particularly,the grid target has a dark chrome opaque metallic coating on a flashed,opal white translucent substrate. A uniform distance between holes mayvary, however it is understood that pinholes have to be sufficientlyspaced apart so they will not blur during examination of the scope.Preferably, this distance is 2.5 mm, whereas a diameter of each holedoes not exceed 45 microns. Each of the holes is positioned in a centerof a respective square. Based on this particular structure a variety ofmeasurements can be easily made by the CPU that uses the algorithms asexplained in greater detail herebelow.

After the endoscope has been mounted to the support station 34 andplaced in a testing position, as explained in U.S. application Ser. No.09/563,866 filed concurrently with this Application, the distal end ofthe rigid endoscope 50 is positioned across the grid target 62illuminated from behind by a first lamp 69, as seen in FIG. 3. The lampis automatically turned on for a predetermined period of time, forexample, 60 seconds during which the endoscope can be focused.

Perhaps, the very basic test without which many of the tests cannot beproperly performed is the field of view test. The apparatus of theinvention is designed to measure scopes having fields of view up to120°. It is easy to calculate this angle by counting the number ofpinholes displayed on the image which is grabbed by the CCD 58 and seenon the monitor and knowing the distance between the distal end of theendoscope and the grid.

Particularly, as shown in FIG. 5, an imaged area 70 can be determinedaccording to the formula:

A=Ns²

Where N is the number of pinholes and s is the spacing between pinholes.Since endoscopes have a circular field of view, the radius of the fieldbeing imaged can be determined:

 r=A/n=Ns²/π

where r is the radial height of the field being imaged. The field ofview can then be determined:

tan(fov/2)=r/d=s/dN/π

fov=2tan⁻¹(s/dN/π)

where fov is the field of view and d is the grid or nominal objectdistance from the distal end 53 of the endoscope to the grid target 62.

The grid distance and the image quality of the scope to be tested canlimit this test. If the grid distance is too short then too few pinholeswill be imaged and the accuracy of the measurement will suffer. If thegrid distance is too large the pinholes at the edge of the field of viewwill be visible, in which case there are no pinholes to image wherethere is still field of view. Based on experimental data, some generallygood object distances are:

approximate field of view good object distances less than 80° 45 mm80-90° 35 mm 90-108° 25 mm 108° 15 mm

As will be explained below, the apparatus is capable to work in acomparative mode when nominal values of a standard endoscope, such as anominal object distance, is stored in database. The apparatus can beused in a new endoscope mode and a non-comparative mode, wherein theabove listed distances can be a reliable factor for proper measurements.The results of the test are illustrated in a test result table 150 ofFIG. 13 and, in case of the comparative mode of operation of the system20, an additional indication of whether the endoscope is failed orpassed is illustrated in a right column P/F.

As shown in FIG. 6, the geometrical distortion is measured by imagingthe grid 62 and recording the position of each visible pinhole. In idealendoscope, an optical center OC of the image coincides with itsgeometrical center GC. By determining the location of the pinholes andby calculating where those locations would be if there were nodistortion, the latter can be calculated.

Particularly, by assuming that the optical center OC of the image isundistorted, an “undistorted” location for each of the imaged pinholescan be compared with the actual position, and the percentage distortionat each object point is measured:

% D=(h_(d)/h_(u)−1)×100%

where % D is the percentage distortion of the point, h_(d) is thedistorted distance from the optical center of the image to the pinhole,and h_(u) is the distance from the optical center to the pinhole ifthere were no distortion.

Next the percentage distortion is graphed as a function of normalizedimage height and a standard polynomial curve fit. As shown in FIG. 6A,the visible field is a polynomial function of the percentage ofdistortion. From this distortion at any desired height ĥ, which is thenormalized object height corresponding to a visible field of image view,can be determined. As shown in FIG. 13, the distortion of the endoscopeas tested can be compared with a nominal value of the standardendoscope. The 1.0 field is an optical term defined by an edge of thefield of view, whereas the other measurement is given for a smallerregion, which is, in this case, 0.7.

The image quality test at a single distance for the entire field of viewis performed by imaging the grid 62 illuminated by the lamp 68 and usinga method of the point spread function (PSF). By measuring the pointspread function the image quality at each point is measured. Basically,this test indicates how sharp the image of each illuminated pinhole is.Every imaged point is spread out to a certain various degree because theendoscope does not make a perfect image, as shown in FIG. 7. The lessblurry a region R is the better sharpness of this particular point is.Conversely, the wider the region R is the worse the image is. Assumingthat each pinhole is infinitely small, then by measuring how big thepinhole is, it is possible to evaluate how this particular pinholespreads out. Clearly, based on a PSF it is possible to calculate amodulation transfer function (MTF) for each of these points. Howeverthis is a lot of data to be processed.

In accordance with the invention, the system is capable of evaluating aspot size or region R for each pinhole by calculating relativebrightness within this region. Thus, simply assuming that everythingbrighter than a certain empirical threshold value is a part of a spot,the size of this spot is evaluated and color coded and shown on thescreen. Thus, blue indicates the best performance, then turquoise,orange, yellow, green and red indicate poor performance and blackindicates no imaging points were found—meaning the performance is verybad.

Specifically, turning to the top row of photographs TP in FIG. 13, it ispossible to evaluate the overall image quality and the image quality inthe center of the image of the tested endoscope by comparing it with thestandard endoscope. Also, it is possible to evaluate the percentage ofthe image that is “red”, and finally, to evaluate the percentage of theimage that is black. Based on this evaluation, the performance of thetested endoscope can be reliably measured.

Both the single pinhole target and the grid can perform the depth offield test. To utilize the grid, all but a single pinhole locateddirectly in line with the theoretical optical axis of the endoscope areturned off. This is the only test when the carousel is displaceablerelative to the distal end of the endoscope 50 at predefined objectdistances to measure the size of the image spot. Larger spots indicatepoorer performance. The depth of field is defined as the object distanceat which the spot size is less than a predetermined value. The depth offield is interpolated from the spot sizes measured. If the range ofobject distances measured does not bound the depth of field, words like“greater than”, “less then”, or “none” will appear in the Depth of FieldDisplay 69 shown in FIG. 13. The actual spots from the scope beingtested are displayed along with simulated spots from a standard scope ifa comparative mode of operation is selected. As is seen in FIG. 13, thesimulated spots are actually circles with the same area as the originalspots. They give no indication of the shape of the original spots. Inaddition, the spots are color coded and, as is previously indicated,blue indicates the best performance, whereas red illustrates the poorestone.

The available object distances are limited because if the objectdistance chosen is too far from the best focus distance or if the scopetransmission is too dim, then the system 20 will not be able to detectthe pinhole resulting in erroneous measurements. As shown in FIG. 13,the numbers across the bottom of a screen are the object distances atwhich the images directly above them were obtained.

The same result in measuring the field view can be achieved by utilizingthe single pinhole target 66 illuminated by a fiberoptic cable 72 whichis plugged in a light source 74, as diagrammatically shown in FIG. 3.

Both the grid 62 and the single pinhole target 66 can also be utilizedto perform the angle of view test. To utilize the grid 62 all of thepinholes have to be turned off except for the one which is located inthe center of the grid. An angle of view of an endoscope, as shown inFIG. 8, is defined as the angle formed by two rays which share a commonendpoint at the center of the entrance pupil 80 of the endoscope 50. Afirst ray 76 extends in the z-direction, and the second ray 78 extendsin the precise direction of the geometrical center (GC) of the endoscopefield of view. It should be noted, therefore, that the angle of viewmeasurement does not precisely define the direction of view.

Referring to FIG. 9, if the endoscope was perfect, an image of thesingle pinhole 82 should be in the geometrical center of the image.However, it is hardly ever the case primarily because of manufacturingdefects. As seen in FIG. 9, the pinhole image 82 is spaced from thegeometrical image center GC at distance p and forms an angle y with thez direction which are converted from image distances to real worlddistances using conversion factors calculated during the field of viewand distortion measurements. Using straightforward trigonometry theangle of view φ can be easily calculated.

FIG. 10 summarizes the above described five tests that can be performedusing the grid target 62. Thus, the lamp 69 positioned on the carouselin an alignment position with the grid target illuminates it frombehind. The carousel then rotates into the nominal field of view of astandard endoscope to selectively perform any combination of the fivetests, the results of which are displayed on the screen of the monitor.It should be remembered that the depth of field and angle of view testscan be performed by either the single pinhole target at 92 or the gridtarget. As mentioned above if the single pinhole target is utilized,then the fiber optic cable 74 connects this single pinhole target withthe source of light 74 located at a distance from the carousel.

As has been mentioned before, the system 20 is able to test a KarlStrorz endoscope by comparing it to a standard one of the same typewhich is stored in the database by selecting this mode of operation. Inthis case all the measured values are compared with a set of standardsparameters at 94.

It is also possible to compare an endoscope other than Karl Storz to ora scope that is not in the data base and then compare it to a standardKarl Storz endoscope which is believed to be analogous to the tested oneupon selecting this mode at 96. Finally, it is possible to test a scopewithout comparison to any other scope by simply introducing valuesaccording to the user's experience and knowledge 90. Regardless of themode selected by the user, the results will be displayed at 100.

According to another aspect of the invention, a bifurcated light guide102, shown in FIG. 11 is used to measure a percentage light transmissionthrough illumination fibers.

Specifically, the bifurcated light guide is fixed to a light source 104(FIGS. 3 and 11) in such a way that the relative illumination througheach output of bifurcated ends 108 and 110 cannot vary. The firstbifurcated end 108 is plugged in a post 112 juxtaposed with the carousel30 (FIG. 3), whereas the second bifurcated end 110 is connected to theendoscope 50, as diagrammatically shown in FIG. 11. Upon turning thelight source on and selecting this test, the carousel 30 is rotated todisplace the detector 64 in a position where it is aligned with thefirst end 108 and where it reads an output of the first end. Thecarousel is then turned to bring the detector 64 into the nominal fieldof the standard scope wherein the detector reads the output of theendoscope. The percentage light transmission through the illuminationfibers can then be calculated:

% T=y O_(s)/O_(b)

where O_(s) is the output of the endoscope, O_(b) is the output of thefirst bifurcated end 108, and y is the ratio of light out of thebifurcated light guide end 108 to the light out of the end that attachesto the scope.

According to still another aspect of the invention, the system 20 iscapable of performing a relative light transmission test through animaging system including a system of lenses by using the white target60. The white target has approximately the same dimensions as the gridtarget and is made of opal glass having a piece of diffuse material,such as paper. Similarly to the grid target, the white target isslidably supported by a respective frame 114 (FIG. 3) and is alignedwith and illuminated by a respective light source 116 (FIG. 3) mountedon the carousel 30.

FIG. 12, illustrates a flow chart for relative imaging systemtransmission showing, in general terms, how much light transmittedthrough the endoscope is lost. The test is performed by first attachingone of the ends of the bifurcated light cable to a socket formed on adistal end of the endoscope and turning the light on at 116. Thebrightness of the light source is measured by a photo detector,preferably a silicone photodiode, rotatable toward the other unattachedend of the light cable introduced between the distal end of the scopeand the carousel at 118. Then, after the photodiode is rotated tonominal field of view o the tested scope at 120, it measure output ofthe endoscope at 122. Both measurements are stored at 124, and a ratiois determined by the CPU upon dividing the measured output of the scopeby the output of the unattached light guide at 126. This result isfurther multiplied by a known calibration factor at 130 with the finalresult displayed at 132 in the table of FIG. 13.

The white target can also be used in testing an illumination profiletest that shows the relative intensity of the illumination of the whitetarget 60 across the field of view of the endoscope 50. Basically, theillumination profile is a fall off of light from the center to the edgeof the field of view of the endoscope. To perform this test the whitetarget is illuminated by the fibers of the endoscope itself byconnecting it to the bifurcated end 110 of the light guide, which isconnected to the source of light 104.

In practical terms, it is always desirable that the edges of the fieldof view of an endoscope used by a surgeon are illuminated and if this isnot the case, then this endoscope should not be used in a surgicalprocedure. The bottom representations BP of photographs of FIG. 13display pictures showing the relative illumination, as seen at thecamera 58, across the field of view of the tested and standardendoscopes. An array of concentric circles 134, which are white at theoriginal photographs, are equidistantly spaced apart contour lines ofimage brightness. A circle 136 indicates the center of the illuminationdistribution. A square 138 is indicative of the dimmest location on the“edge” of the image, while a square 140 is the brightest location on the“edge” of the image. A first pair of cross lines 142 goes through thecenter of the image, while another pair of cross lines 144 is centeredat the center of the image. If the illumination system of the endoscopeincluding fibers have been damaged or, more likely, poorly designed, thephotograph could have a big bright spot in the middle of the imagewhereas the edges would be dark. By comparing the photographs of thetested and standard endoscopes, as seen in FIG. 13, a user may concludethat the illumination system of the tested scope is acceptable.

Still another test, which the system 20 can perform, is an imageanalysis when the camera 58 is focused to infinity, as shown on a leftpicture (LP) of the middle row of FIG. 13. This indicator displays apicture representing the image quality across the field of the endoscopewhen the camera and endoscope coupler are set to image a distant object.On a screen this is image is color coded with blue regions representingareas of highest quality, red representing areas of lowest quality andblack representing areas where no image data has been found. Thisanalysis can be compared with a picture representing the image qualityof a standard scope when the camera is focused to image a distantobject. Similarly to the above described color codes, this picture hasblue and red regions indicating poor high quality and poor qualityareas, respectively.

This invention is not to be limited by the embodiment shown in thedrawings and described in the description, which is given by way ofexample and not of limitation, but only in accordance with the scope ofthe appended claims.

What is claimed is:
 1. An apparatus for evaluating performance of a testendoscope, comprising a source generating a beam of light entering adistal end of the test endoscope; a grid consisting of a plurality ofpinholes intercepting the beam of light at a predetermined distance fromthe distal end for evaluating field of view, image quality, distortionand depth of field of the test endoscope.
 2. The apparatus defined inclaim 1 wherein the pinholes of the grid are uniformly spaced from oneanother at a predetermined distance, each having a predetermined uniformdiameter.
 3. The apparatus defined in claim 1 wherein the grid furtherperforms an angle of view test wherein a one pinhole of the plurality ofpinholes is illuminated.
 4. The apparatus defined in claim 1, furthercomprising database storing a set of parameters of the tests conductedon a standard endoscope and a central processing unit which includes acomparator comparing the results of field of view, image quality,distortion, depth of field and the angle of view tests of the test andstandard endoscopes.
 5. The apparatus defined in claim 1 wherein thesource and the grid are mounted on a rotatable carousel and are alignedwith one another, the carousel supporting a second source of lightaligned with a diffuse but translucent white target, a single pinholetarget and a photo sensor for performing a percentage light transmissiontest through the test endoscope.
 6. The apparatus defined in claim 1wherein the grid is displaced to a nominal field of view of the standardendoscope at the predetermined distance from the distal end of the testendoscope and is illuminated to have a number of pinholes displayed on amonitor of the central processing unit, wherein a field of view of thetested endoscope being calculated as 2tan(s/dN/π), where d is thepredetermined distance between a distal end of the tested endoscope andthe grid, s is the uniform spacing between the pinholes and N is thenumber of pinholes.
 7. The apparatus defined in claim 1 wherein the gridis displaced to a nominal field of view of the standard endoscope toperform the geometrical distortion test at each pinhole of the grid seenon the monitor by determining a location of each pinhole of the testedendoscope and by comparing it with a location of the respective pinholeof an ideal, undistorted grid.
 8. The apparatus defined in claim 1wherein the grid is illuminated to have the image quality of thepinholes of the entire field of view seen on the monitor, the imagequality being measured by calculating a point spread function or MTF foreach of the pinholes and by comparing it with a point spread function orMTF of the respective pinhole of the standard endoscope.
 9. Theapparatus defined in claim 6 wherein the monitor displays a table ofresults including a numerical value of the distortion test, the angle ofview test and of the field of view test, the table further having a“pass/fail” column indicating a pass/fail result in response to arespective signal generated by the comparator of the central processingunit upon comparing the results of the respective test of the test andstandard endoscope.
 10. The apparatus defined in claim 8 wherein themonitor further displays a multi-colored visual image upon taking theimage quality test, the image having regions colored in blue indicatingthe best performance, regions colored in turquoise, green, yellow,orange and red indicating a poor performance of the tested endoscope andregions colored in black indicating the worse performance.
 11. Theapparatus defined in claim 10 wherein a percentage of red and blackregions is calculated by the central processing unit generating a signalindicating a “pass/fail” result upon comparing this percentage with theone of the standard endoscope.
 12. The apparatus defined in claim 1wherein the depth of field is measured by displacing the grid at aplurality of predetermined distances with respect to the distant end ofthe tested endoscope to have an actual spot size of the pinholesdisplayed at each of the predetermined distances and compared with apredetermined value.
 13. The apparatus defined in claim 12 wherein theactual size of the pinholes of the tested endoscope at each of thepredetermined distances is compared with a simulated spot from thestandard endoscope displayed on the monitor.
 14. The apparatus definedin claim 12 wherein each spot is color coded with blue identifying anacceptable depth of field and red identifying an unacceptable depth offield.
 15. The apparatus defined in claim 5 wherein the white target isa plate made of opal glass having a piece of diffuse white paper. 16.The apparatus defined in claim 15 wherein the white target isilluminated by a second source of light upon being displaced to thenominal angle of view of the standard endoscope to perform a relativebrightness test of the test endoscope calculated by the centralprocessing unit as a ratio of the brightness at the proximal end of theendoscope to the brightness at the distal end thereof.
 17. The apparatusdefined in claim 16 further comprising a camera attached to a proximalend of the endoscope and a silicone photodiode juxtaposed with thedistal end of the test endoscope for measuring the brightness of theimage of the white target, the camera measuring the brightness at theproximal end of the endoscope.
 18. The apparatus defined in claim 17wherein the ratio of the brightness at the proximal end to thebrightness at the distal end is compared to a ratio of the standardendoscope by the comparator with numerical values appearing on themonitor in response to a signal generating by the comparator uponcomparison.
 19. The apparatus defined in claim 15 wherein the whitetarget is displaced to the nominal angle of view of the standardendoscope to perform an illumination profile test indicating relativeintensity of the illumination of the white target across the field ofview of the test endoscope.
 20. The apparatus defied in claim 19 whereinthe white target is illuminated by a source of light spaced from thecarousel and connected to the endoscope by a bifurcated fiber opticcable which is designed to have a uniform light intensity output atfirst and second bifurcated ends thereof.
 21. The apparatus defined inclaim 6 wherein the photo sensor is displaced in a first angularposition, wherein it is aligned with the first bifurcated end of thefiber optic cable to generate a first signal in response to reading anoutput thereof, the photo sensor being displaced to the nominal angle ofview of the standard endoscope in a second position spaced angularlyfrom the first position to generate a second signal in response toreading an output of the test endoscope connected to the secondbifurcated end of the fiber optic cable.
 22. The apparatus defined inclaim 21 wherein a ratio of the second signal to the first signalcalculated by the central processing unit indicates the percentage lighttransmission through the endoscope.
 23. An apparatus for evaluatingperformance of a test endoscope, comprising a source generating a beamof light transmitted through the endoscope; a fiber optic light guideattached by one of opposite ends thereof to the source and having theother end bifurcated, so as one of the bifurcated ends is attached tothe endoscope; a photo sensor rotatable between a first position,wherein it is aligned with another of the bifurcated ends for generatinga first signal corresponding to an illumination output, and a secondposition, wherein the photo sensor is aligned with the endoscope at apredetermined distance therefrom for generating a second signalcorresponding to an illumination output of the endoscope; and acontroller for generating a third signal in response to the first andsecond signals corresponding to a percentage light transmission throughthe endoscope.
 24. The apparatus defined in claim 23 wherein the one andother bifurcated ends of the fiber optic light guide have a uniformoutput.
 25. The apparatus defined in claim 23 further comprising a gridconsisting of a plurality of pinholes intercepting a beam of lightgenerated by a second source of light at a predetermined distance fromthe distal end for evaluating a field of view, an image quality,distortion, depth of field and an angle of view of the test endoscope.26. The apparatus defined in claim 25 wherein the pinholes of the gridare uniformly spaced from one another at a predetermined distance, eachof the pinholes having a predetermined uniform diameter.